Sugar crystallization



Patented Apr. 8, 1952 SUGAR CRYSTALLIZATION George Joseph King, Hewlett, N. Y., assignor to Atlas Powder Company, Wilmington, Del., a

corporation of Delaware No Drawing. Application August 5, 1950, Serial No. 177,965

The present invention relates to improvements in sugar crystallization.

It is an object of the invention to improve the process for producing crystalline sugar.

Another object is to improve the rate of crystallization of sugar from supersaturated solutions.

Another object is to increase the yield of crystals in a sugar crystallization process.

A further object is to improve the quality of sugar crystals in respect of color, texture and dryness.

The above and other objects will become apparent in the course of the following description.

The conventional procedure of producing sugar from cane or beet involves repeated concentrations and crystallization. Some of these steps require extended lengths of time, as much as 72 hours, to attain practical completion of crystallization. The length of time is a major objec: tion to the existing processes requiring large capital investment in materials in process and processing equipment. It has also been recognized that even holding the crystallization step over a prolonged period does not remove all of the valuable sugar and much of the sugar in the mother liquor is sacrificed as a low-grade byproduct of sugar refining.

Generally similar processes are employed in the production of the various commercial forms of crystalline dextrose. The improvement of these processes is also within the scope of. this invention.

A related problem is recognized in the so-called soft sugar phase of sugar manufacture in that these soft sugars or brown sugars are difficult to obtain in a satisfactory condition. A common objection to the soft sugars is their tendency to block into a solid mass. Other objections noted are loss of bloom and absence of free fiowing characteristics identified as crawl in the trade.

In accordance with the present invention it has been found that substantial improvements in crystalline sugar products are obtained when the mother liquor or adherent molasses is removed from the crystals in the presence of certain nonionic surface active agents hereinafter described. To obtain these improvements the said surface active agents can be introduced at any stage of the process up to and including the crystal purging step. In addition to the improvement of the ultimate crystalline product, other advantages in the crystallization itself are obtained where the surface active agent is introduced before or during crystallization. Thus, the invention can be practised by adding the surface active agent dur- 14 Claims. (01. 12758) ing the boiling of the sugar liquor, during crystallization, during the dumping or spinning of the massecuite, or during the crystal purging (by addition to the purge water).

In the presence of small amounts of the surface active agents here employed sugar crystallizes from solution at an increased rate and has been observed to form a drier and whiter product. The improvement in the crystallization process therefore makes it possible to reduce the time required for growing a given quantity of sugar crystals or, under some circumstances, to grow a larger crop of sugar crystals in a given length of time. The crystalline sugar product is of better quality particularly in the soft or brown grades.

The nonionic surface active agents employed in the practice of the invention may be selected from the following groups: (1) partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule; (2) polyoxyalkylene ethers of partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; (3) polyoxyalkylene esters of long chain fatty acids wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; and (4) long chain fatty acid esters of polyoxyalkylene ethers of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each. The term long chain fatty acid is used herein to identify the fatty acids which have from 12 to 18 carbon atoms per molecule.

Examples of surface active agents of the class identified as (1) above include glycerol monooleate, pentaerythritol monolaurate, mannitol dioleate, sorbitan monolaurate, sorbitan monostearate, sorbitan monopalmitate and glucose monostearate. The polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule, therefore, include the polyhydric alcohols, the cyclic inner ethers of polyhydric alcohols and the simple sugars.

Surface active agents of the type identified as (2) above include 10 polyoxyethylene glycerol monopalmitate, 15 oxyethylene pentaerythritol monomyristate, 10 polyoxyethylene-lO polyoxypropylene sorbitan monostearate, 20 polyoxyethylene sorbitan monostearate, 40 polyoxyethylene mannitol distearate, 20 polyoxypropylene sorbitan monostearate, l0 polyoxyethylene sorbide monolaurate, and 30 polyoxyethylene glucose monostearate. The Arabic numeral preceding the name of the compound indicates the average number of oxyalkylene groups per molecule of the compound. As well understood in the chemical arts, compounds of this type are prepared by reacting the partial ester with ethylene oxide propylene oxide or mixtures of ethylene and propylene oxides in proportions to produce the average number of oxyethylene groups desired per molecule of the finished polyoxyalkylene ether. Alternatively, a preformed polyalkylene glycol of an average oxyalkylene unit content corresponding to that desired is condensed by conventional etherification reaction with the partial ester.

Surface active agents of the type identified as (3) above include 8 polyoxyethylene monostearate. l5 polyoxyethylene distearate, 20 polyoxyethylene monooleate, 20 polyoxyethylene stearate oleate, 6 polyoxyethylene monolaurate, l polyoxypropylene monooleate, and polycryethylene-5 polyoxypropylene monolaurate. Compounds of this type may be prepared by the esterification of a polyalkylene glycol containing the required number of oxyalkylene groups or by the reaction of alkylene oxide and the indicated fatty acid. The latter reaction produces a monoester which can, if desired, be completely esterified by reaction with another mol of the same or a different fatty acid.

Surface active agents of the type indicated as (4) above include the monolaurate of hydroxyethyl glycerol, the monopalmitate of polyoxyethylene pentaerythritol, the dioleate of 6 polyoxyethylene mannitol, the dioleate of 5 polyoxypropylene mannitol, the hexaoleate of polyoxyethylene sorbitol, the pentastearate of 40 polyoxyethylene sorbitol and the monostearate of 6 'polyoxyethylene glucose. The compounds of this group are distinguished from those of type (2) in that the polyhydroxylic compound is first reacted with alkylene oxide or an alkylene or polyalkylene glycol to form the oxyalkylene or polyoxyalkylene ether which is thereafter esterifled with the indicated fatty acid.

Mixtures of surface active agents of one or more of the types described are contemplated for use in practising the invention.

Preferred surface active agents for use in accordance with the invention are the polyoxyethylene compounds of types (2), (3) and (4), which contain at least 6 oxyethylene groups for each fatty acid radical. These compounds are readily dispersible in the sugar solutions.

The amount of surface active agent required to accomplish the intended improvement varies with the particular agent selected, the particular process in which it is used and the manner in which it is applied. From 0.01% to 0.5% sur-' face active agent based on sugar solids is generally preferred. In order to facilitate mixing of the surface active agent with the concentrated liquors it may be found desirable to disperse or dissolve the surface active agent in a small quantity of water or a more dilute sugar solution and distribute this throughout the concentrated solution. Additional stirring or mixing may be desirable to hasten the dispersion of the added material.

Where the surface active agent is added to the purge water the preferred concentrations are from 0.1% to 1.0% in the water.

The following examples are illustrative of the process of this invention.

Example I The effect of a surface active agent of the class defined on the crystallization of sucrose is illustrated by the following small scale laboratory test:

A sucrose syrup 1.04 supersaturated at 25 C. was modified by adding to it 0.3% of 20 polyoxyethylene sorbitan monostearate, based on the weight of sugar in the syrup. A 10 gram sample of thetreated syrup was placed in a test tube and seeded with 6X-sugarat a 1 :30 ratio. The change in concentration of the syrup as crystallization occurred at 25 'C. was determined by observing the refractive indices of the syrup at 1 minute intervals. After 15 minutes the syrup showed that 66.5% of the sugar in excess of the saturation value at 25 C. had crystallized.

A similar test run without the addition of the surface active agent showed only 19% crystallization in the same time.

Example II A test similar to that described .in Example I was performed using 0.3% of '20 polyoxyethylene sorbitan monolaurate instead of the monos'tearate of Example .1. After crystallizingfor 15 minutes, 44% of the sugar in excess of the saturation value had crystallized.

Example III Example IV In a beet sugar process the invention can be practiced as follows:

To a green syrup in the vacuum pan 0.1 sorbitan monostearate is added based on the sugar solids in the pan. The syrup is boiled in the agitation produced thereby serves to disperse the surface active agent. The crystalline sugar product is recovered in the conventionalmanner and the mother liquor is passed on to be boiled for another strike of sugar. The mother liquid contains the added surface active agent and its functions are therefore carried through to the subsequent stages of the process.

Example V In a corn sugar refining process the invention can. be practiced as follows:

To a corn syrup being boiled in a vacuum pan is added 0.05% of -8-polyoxyethylene monostearate based on the weight of sugar in the pan. After concentration the syrup is drawn off, seeded, crystallized and spun.

Example VI In the production of brown sugar the invention can be applied thus:

A cake of brown sugar in the centrifuge .is purged with Water containing 0.2% by weight of 20-polyoxyethylene monostearate. The sugar is then recovered from the centrifuge in the usual manner.

Many variations in the details of the process will be apparent to those skilled in this art without departing from the invention which is .defined in the following claims.

What is claimed is:

1. In the process for producing crystalline sugar the improvement which consists in removing the mother liquor from the crystals in the presence of a surface active agent selected from the group consisting of: (1) partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule'; (2) polyoxyalkylene ethers of partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; (3) polyoxyalkylene esters of long chain fatty acids wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; and (4) long chain fatty acid esters of polyoxyalkylene ethers of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each.

2. The process of claim 1 wherein the sugar is cane sugar.

3. The process of claim 1 wherein the sugar is beet sugar.

4. The process of claim 1 wherein the sugar is dextrose.

5. The process of claim 1 wherein the sugar is brown sugar.

6. In the process for producing crystalline sugar the improvement which consists in growing the sugar crystals in the presence of a surface active agent selected from the group consisting of (1) partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule; (2) polyoxyalkylene ethers of partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; (3) polyoxyalkylene esters of long chain fatty acids wherein the oxyalkylene groups have from 2 to '3 carbon atoms each; and (4) long chain fatty acid esters of polyoxyalkylene ethers of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each.

7. The process defined in claim 6 wherein the said surface active agent contains at least 6 oxyethylene groups per fatty acid radical.

8. The process of claim 6 wherein the surface active agent is 20-polyoxyethylene sorbitan monostearate.

9. The process of claim 6 wherein the surface active agent is introduced into the crystallizer.

10. The process of .claim 6 wherein the surface active agent is present in the amount of 0.01 to 0.5 by weight of sugar solids.

11. In the process for making a soft sugar the improvement which consists in purging the spun cake with Water containing a surface active agent selected from the group consisting of: (1) partial long chain fatty acid esters of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule; (2) polyoxyalkylene ethers of partial long chain fatty acid esters of polyhyclroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; (3) polyoxyalkylene esters of long chain fatty acids wherein the oxyalkylene groups have from 2 to 3 carbon atoms each; and (4) long chain fatty acid esters of polyoxyalkylene ethers of polyhydroxylic compounds which have from 3 to 6 carbon atoms per molecule wherein the oxyalkylene groups have from 2 to 3 carbon atoms each.

12. The process of claim 11 wherein the surface active agent contains at least 6 oxyethylene groups per fatty acid radical.

13. The process of claim 11 wherein the surface active agent is 20 polyoxyethylene sorbitan monostearate.

14. The process of claim 11 wherein the surface active agent is present in the amount of 0.1% to 1.0 in the water.

GEORGE JOSEPH KING.

REFERENCES CITED UNITED STATES PATENTS Name Date Spreckels et al May 13, 1902 Number 

6. IN THE PROCESS FOR PRODUCING CRYSTALLINE SUGAR THE IMPROVEMENT WHICH CONSISTS IN GROWING THE SUGAR CRYSTALS IN THE PRESENCE OF A SURFACE ACTIVE AGENT SELECTED FROM THE GROUP CONSISTING OF: (1) PARTIAL LONG CHAIN FATTY ACID ESTERS OF POLYHYDROXYLIC COMPOUNDS WHICH HAVE FROM 3 TO 6 CARBON ATOMS PER MOLECULE; (2) POLYOXYALKLENE ETHERS OF PARTIAL LONG CHAIN FATTY ACID ESTERS OF POLYHYDROXYLIC COMPOUNDS WHICH HAVE FROM 3 TO 6 CARBON ATOMS PER MOLECULE WHEREIN THE OXYALKYLENE GROUPS HAVE FROM 2 TO 3 CARBON ATOMS EACH; (3) POLYOXYALKYLENE ESTERS OF LONG CHAIN FATTY ACIDS WHEREIN THE OXYALKYLENE GROUPS HAVE FROM 2 TO 3 CARBON ATOMS EACH; AND (4) LONG CHAIN FATTY ACID ESTERS OF POLYOXYALKYLENE ETHERS OF POLYHYDROXYLIC COMPOUNDS WHICH HAVE FROM 3 ALKYLENE GROUPS HAVE FROM 2 TO 3 CARBON ATOMS EACH. 